“Prospective mothers should take common sense preventive measures, such as getting flu shots prior to and in the early stages of pregnancy and avoiding contact with people who are symptomatic,” said Alan Brown, of Columbia University and New York State Psychiatric Institute,according to the NIH study.

“In spite of public health recommendations, only a relatively small fraction of such women get immunized. The weight of evidence now suggests that benefits of the vaccine likely outweigh any possible risk to the mother or newborn.”

The study found that the nearly fourfold increased risk was due to influenza infection at any time during pregnancy—but, evidence suggested a slightly higher risk if the flu occurred during the second or third trimesters.